Hydraulic drive systems have been used to drive a feed auger and spinner of a spreader typically carried by a vehicle for spreading a road surface treatment material, such as sand or salt, across a road being traversed by the vehicle. The feed auger delivers the road surface treatment material from a supply thereof, such as a hopper, to the spinner which distributes the material across a road surface.
Many of these systems are designed as self-contained units that can be mounted in the bed of a pickup dump truck. Pressurized hydraulic fluid is supplied by a hydraulic pump typically driven by a gasoline engine. Cab-mounted, manually operated hydraulic flow control valves have been used to adjust the rotary speeds of the material conveyor (auger) and spinner fan (spinner).
Electrically-operated hydraulic valves have been used for spreading applications. These systems have used a parallel type flow configuration for supplying hydraulic fluid to the hydraulic motors that drive the auger and spinner. These systems require relatively large pumps to supply adequate flow to the auger and spinner motors.
U.S. Patent Application Publication No. 2005/0204587 discloses a microprocessor-controlled hydraulic system for snow-ice removal trucks that uses digital hydraulic valving control responsive to the instantaneous speed of the truck. According to this document, a binary form of digital valving removes a requirement for vulnerable feedback lines and associated sensors. As disclosed, the hydraulic motors for driving the auger and spinner are serially connected. The valves are either in an open position or a closed position depending on the desired amount of hydraulic flow. When no hydraulic pressure is to be supplied to the auger and/or spinner motors, i.e. when the digital control valves are all closed, hydraulic flow is routed back to reservoir by a bypass valve. When the bypass valve is open, pressure cannot buildup at the inlets to the auger and spinner motors.